1. Field of the Invention
The present invention relates to a semiconductor integrated-circuit capacitor and a method of manufacturing the same.
2. Description of the Related Art
As a type of semiconductor device adapted for information storage, there is a dynamic random access read-write memory (DRAM) whose storage cells are based on transistor-capacitor combinations. In a capacitor used in a storage cell in such a DRAM, as its electrodes use is made of a material, such as polysilicon, tungsten (w), molybdenum (Mo), or aluminum (Al). As an insulating film sandwiched between the two electrodes of the capacitor, serving as the capacitor insulating film (dielectric film), a silicon oxide film is used.
With recent rapid large-scale integration of such semiconductor devices, it has been required that the capacitance of capacitors be increased. With a conventional capacitor structure, this requirement will be met by reducing the thickness of silicon oxide film used as an insulating film to a great extent because silicon oxide is low in permittivity or dielectric constant. However, reducing the thickness of the capacitor insulating film too much will result in an increase in current leakage.
For this reason, instead of reducing the thickness of the capacitor insulating film, the use of an insulating film having higher permittivity than the silicon oxide film is now being considered. Specifically, metal compounds including perovskite dielectric material, such as tantalum pentoxide, PZT(Pb(Ti, Zr)O.sub.3), etc., are under consideration. The dielectric constant of tantalum pentoxide film is approximately seven times as high as the dielectric constant of silicon oxide film.
On the one hand, however, these metal compounds exhibit high permittivity, but on the other hand they are small in forbidden band width (band gap) and hence have a poor insulating capability. Consequently, the use of these materials as a capacitor insulating film would also cause an increase in leakage current. In other words, the insulating film formed of such a high-permittivity material as described above has a considerably poor capability of retaining charges, which reduces the charge retaining capability of capacitors and hence decreases the reliability of DRAMs.